Recent Developments in Electroanalytical Chemistry of Cephalosporins and Cefamycins

Cephalosporins (I, R⁴ = H) and cefamycins (I, R⁴ = OCH₃) are antibiotics with a broad spectrum of antimicrobial and antibacterial properties. These compounds contain a β-lactam ring which is fused with a six-membered dihydrothiazine ring bearing substituents R¹ and R² in the side-chains at C-3 and C-7 (I)(Table I).     

Copper-catalyzed one-pot synthesis of imidazo/benzoimidazoquinazolinones by sequential Ullmann-type coupling and intramolecular C-H amidation

A simple, practical, and highly efficient copper-catalyzed one-pot synthesis of imidazo/benzoimidazoquinazolinones has been developed. The procedure is based on a sequential copper-catalyzed Ullmann-type N-arylation and aerobic oxidative intramolecular C-H amidation. This method should provide a new and useful strategy for construction of N-heterocycles.     

Aerobic oxysulfonylation of alkynes in aqueous media: highly selective access to β-keto sulfones

The first application of inexpensive commercially available sulfinate salts to produce β-keto sulfones directly from alkynes via aerobic oxysulfonylation has been developed. It is a highly selective (undesired Glaser–Hay homo-coupling and ATRA process totally suppressed) general method of functionalization of alkynes on water at room temperature involving FeCl₃/K₂S₂O₈ catalyzed formation of sulfonyl radicals from sulfinate salts.     

Quaternary ammonium hydroxide-functionalized g-C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols

A new and efficient metal-free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g-C₃N₄ catalyst has been described. The functionalized quaternary ammonium hydroxide (g-C₃N₄-OH) has been prepared from graphitic carbon nitride (g-C₃N₄) scaffold by converting the residual –NH₂ and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion-exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH- form) by post-synthetic modification. The resultant g-C₃N₄-OH was characterized by XRD, FTIR, field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), N₂ adsorption/desorption isotherms, and acid–base titration. Tested as solid-base catalysts, the g-C₃N₄-OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g-C₃N₄-OH solid-base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%).     

Highly Diastereoselective and Regioselective Copper‐Catalyzed Nitrosoformate Dearomatization Reaction under Aerobic‐Oxidation Conditions

An unprecedented copper‐catalyzed acylnitroso dearomatization reaction, which expands the traditional acylnitroso ene reaction and acylnitroso Diels–Alder reaction to a new type of transformation, has been developed under aerobic oxidation. Intermolecular and intra‐/intermolecular reaction modes demonstrate an entirely different N‐ or O‐acylnitroso selectivity. Hence, we can utilize this reaction as a highly diastereoselective access to a series of new pyrroloindoline derivatives, which are important structural motifs for natural‐product synthesis.     

Merging Aerobic Oxidation and Enamine Catalysis in the Asymmetric α‐Amination of β‐Ketocarbonyls Using N‐Hydroxycarbamates as Nitrogen Sources

We describe herein an unprecedented asymmetric α‐amination of β‐ketocarbonyls under aerobic conditions. The process is enabled by a simple chiral primary amine through the coupling of a catalytic enamine ester intermediate and a nitrosocarbonyl (generated in situ) derived from N‐hydroxycarbamate. The reaction features high chemoselectivity and excellent enantioselectivity for a broad range of substrates.